Biophysikalische Bildgebung

Molecular crowding is an inherent feature of cell interiors. Synthetic cells as provided by giant unilamellar vesicles (GUVs) encapsulating macromolecules (polyethylene-glycol and dextran) represent an excellent mimetic system to study membrane transformations associated with molecular crowding and protein condensation. Similarly to cells, such GUVs exhibit highly curved structures like nanotubes. Upon liquid-liquid phase separation their membrane deforms into apparent kinks at the contact line of the interface between the two aqueous phases. These structures, nanotubes and kinks, have dimensions below optical resolution. Here, we studied them with super-resolution stimulated emission depletion (STED) microscopy facilitated by immobilization in a microfluidic device. We demonstrate the cylindrical nature of the nanotubes based on the superior resolution of STED and automated data analysis. The deduced membrane spontaneous curvature is in excellent agreement with theoretical predictions. Furthermore, we were able to resolve the membrane kink-like structure as a smoothly curved membrane demonstrating the existence of the intrinsic contact angle, which describes the wettability contrast of the encapsulated phases to the membrane. Resolving these highly curved membrane structures with STED imaging provide important insights in the membrane properties and interactions underlying cellular activities.